As a finishing material such as a wall surface, a pillar surface or a ceiling surface composed of a calcium silicate board or a gypsum board, wall papers of poly(vinyl chloride) which are easy to apply and have excellent economy have been used widely, but the resulting surface finished by application of wall papers gives poor substantial ventilation. For this reason, the ventilation possessed by the board of the base material is hindered by the wall paper, and this causes dew formation on the surface and brings about the development of molds and the peeling of the wall paper. Furthermore, the wall papers and adhesives used in adhering the wall papers have caused various health hazards.
As a finishing material replacing the wall papers, a wet-type finishing such as stucco and Juraku finish by a plasterer which has ventilation and does not emit noxious substances has been reconsidered. However, since aging is required until the wet-type finishing material is solidified, the term of construction is long, and another problem is that a difference in the ability and experience of the individuals of plasterers is easy to appear. Furthermore, since the number of excellent plasterers is insufficient in recent years, it is impossible to meet the above required demand.
Accordingly, by forming a decorative layer containing calcium carbonate as a main component of stucco on the surface of a board or sheet, the present inventors have developed an architectural material having a design very similar to a plasterer finish of a wet-type finishing material such as stucco or Juraku finish.
For example, the present inventors have provided architectural materials in which a decorative layer containing calcium carbonate as a binding component is formed on the surface of a base material as shown in Japanese Laid-Open Patent Publications Nos. 331831/1995, 244159/1996, 72195/1996 and 41614/1997.
However, the above-mentioned architectural materials develop powderization on the surface of a decorative layer containing calcium carbonate as a binder component formed on the surface of a base layer such as a board or sheet or the surface of the decorative layer has a defect of a low hardness. For this reason, during the transportation of the base material, during a secondary processing, or during the application, the decorative layer is prone to be contaminated or injured, and it has a serious problem in use at a building site.
When the base material is a sheet having flexibility, in addition to the above-problem, the decorative layer is liable to be cracked by bending stress during the transportation, the secondary processing or the application. Such architectural materials are not satisfactory practically.
In order to compensate for the soiling of the decorative layer or the easy injury of the decorative layer, it is considered to protect the surface of a decorative layer of the architectural material, and mount a protective sheet which can be removed easily by a suitable force after application. For example, in a wooden board on which a resin decorative layer is provided on the surface, or in a stainless steel plate in which the surface is mirror-finished, it is known that in order to protect its surface, a protective sheet composed of a sticky sheet is provided.
However, since the surface of the decorative layer containing calcium carbonate as a binder component possesses a powderization portion or has a porous portion, it is difficult to laminate a protective sheet by its intimate adhering force alone with a sufficient peeling strength.
When a strong adhesive agent is used in order to increase the peeling strength with the decorative layer, the peeling adhesion strength of the protective sheet is not stable for the above reason, and if there is a portion having too strong a part, the decorative layer may be damaged when the protective sheet is peeled off, and the sticking agent comes into the pores of the decorative layer and the sticking agent is transferred to the decorative layer and remains there.